Process for transmitting data between entities capable of emitting and/or receiving data

ABSTRACT

The process disclosed is appliable to transmission of data of the multiplexed series type between entities capable of emitting or receiving data, to or from the line. Each entity connected to the line can access all the data flowing in the line, and all the exchanged data are modeled by a distributed data base which is updated and maintianed by the fact that each entity stores and updates a local copy of the corresponding useful part of the data base it contains. Each time an entity is placed in service, a coherence check is carried out to ensure that the emitting and consuming entities interpret data in the same way. The coherence check is carried out by a protocol without prior contact or acknowledgement.

FIELD OF THE INVENTION

The present invention relates to a transmission method of themultiplexed series type which can be used for exchanging informationbetween the sensors, the actuators and programmable automata of aprocedure.

BACKGROUND OF THE INVENTION

Generally, communication between the sensors, actuators and programmableautomata is provided wire to wire, which represents considerable wiringcosts without a real service quality.

The invention relates more particularly to a better adaptedcommunications system which reduces the wiring costs and which permitsthe connection of all industrial equipment included in a control andchecking system and complying with an appropriate standard.

Its objective is to design systems with evolutive modular structuresfrom a limited range of material modules making mass production possibleso as to reduce the costs.

This evolutive modular structure must make it possible to respond to awide range of applications, by software personalization.

SUMMARY OF THE INVENTION

In such a system, the invention proposes a protocol for exchanginginformation between data processing equipment of programmable automatonor industrial computer type, instrumentation equipment of more or lessintelligent sensor or actuator type and operator interfaces ofindividual actuator signalling and control type.

This protocol must be sufficiently general to allow equipment which maybe of different origins to be readily interconnected so as to form anindustrial checking and control system without any problem ofconviviality between these different pieces of equipment.

The information exchanges take place by means of a line capable ofeffecting transmission, without acquittal of the multiplexed series type(for example coaxial cable, optical fibres), between components of thesystem (entities) for receiving or transmitting information from or tothe communication carrier and to ensure physical and logic interfacesbetween the line tools and the application interfaces, line toolsproviding matching of the signals between the components of the systemand the line, and a Bus Arbitrator.

The application interfaces may be of different types and may, forexample, consist of:

reception equipment (logic, analog outputs, interface displays of dataacquisition, specialized equipment, . . .);

transmission equipment which transmits data over the line when requestedto do so, such data consisting of sensor logic or analog acquisitions,controls from programmable automatic devices, interautomata dataexchanges, specialized data required for the application;

reception and transmission equipment which may be the result of acombination of the previously defined equipment but also, for example,intelligent instruments, reflex automata, sequential automata, controlcomputers, maintenance assistance, specialized equipment required forthe application.

Each exchange over the transmission line takes place by a succession:

of a first frame which may for example comprise a preamble, a 16 bitword, . . . , a control block, for example of "CRC" type (cyclic codefor detecting consistency errors of the data), . . . , this framecorresponding to the nomenclature of the data which will be madeavailable on the line, and

a second frame which may for example comprise a preamble, a value, acontrol block, for example of "CRC" type, this frame containing thevalue of the data corresponding to this nomenclature, this word in factrepresenting the contents of the data identified by its nomenclature.

It should be noted that the use of a cyclic code, particularly reliablefor detecting consistency errors of the exchanged information (forexample of "CRC" type), makes it possible to make good the absence of anacquittal procedure in the information exchanges.

Thus, the nomenclature/information pair may be:

the result of an A/D conversion from a sensor;

a control to an analog actuator;

a combination of logic states from sensors;

a combination of logic states to actuators;

a variable internal to an automaton;

the value of a parameter;

any logic combination of 16 bits.

The information exchanges are timed by the Bus Arbitrator whichbroadcasts the nomenclatures cyclically over the line, and take place inaccordance with the following procedure:

the Bus Arbitrator broadcasts a nomenclature;

the station which has this nomenclature recognizes itself;

the station which has recognized itself makes the information associatedwith the nomenclature which has just been transmitted available on theline;

the stations which wish to consume this information previouslyidentified by its nomenclature then read the information transmitted bythe producer station;

the Bus Arbitrator also consumes the information so as to make sure thatthe transaction is carried out correctly and the cycle continues bysending a new nomenclature.

In the case of cyclic traffic, the functions of the Bus Arbitrator maythen be summed up as follows:

controlling the nomenclature to be transmitted as a function of thetransmission frequency of this nomenclature;

verification of the transmission of the data associated with thisnomenclature;

the timing of the frames;

transmission of the new nomenclature;

operating test of the transmission system (detection of errors,collisions, the correct operation of the connected equipment).

The functions of an information receiver may be summed up as follows:

detection of the presence of a nomenclature on the line;

reception of this nomenclature;

recognition of the utility of receiving information associated with thisnomenclature or waiting for a new nomenclature;

reception of the data associated with the nomenclature;

storing of the data associated with the nomenclature which has just beenread.

The functions of an information transmitter can also be summed up asfollows:

detection of the presence of a nomenclature on the line;

reception of this nomenclature;

the recognition of the utility of transmitting the data associated withthis nomenclature or waiting for a new nomenclature;

selection of the data to be transmitted, associated with thenomenclature which has just been read;

transmission of the data associated with the nomenclature.

The information transmitter-receivers group together all the functionsof the previously enumerated information transmitters and receivers.

From the foregoing description it is clear that in accordance with thistransmission system:

Each piece of equipment connected to the transmission line may haveaccess to all the information flowing over this line. By construction,the signal multiplying effect makes it possible to make the informationtransmitted by a subscriber available to all the other subscribers. Thisfeature virtually gives each subscriber the impression of being"connected" to all the information which flows.

Information from a sensor may then be acquired by all the otherequipment connected to the line, as soon as this information istransmitted over the line, the wiring being limited to connection of thesensor to an acquisition card of a subscriber of the line.

The bridging of information between several pieces of processingequipment may take place over the line for the flowrates and therefreshment times are, in most cases, compatible with the real timeaspect of the reflex automata.

The whole of the data exchanged over such a system (essentially cyclicexchanges of state variables) may be modelled by a distributed database, each entity of which, connected to the transmission line, keeps acopy of the data concerning it, either as producer or as consumer.

In fact, this distributed data base, which groups together a collectionof data grouped together by object, is an abstract representation of theinformation which is distributed over the transmission line, so that atall times all the users of an object must have the same perception ofthis object. Such perception is modelled by a frame which applies toeach type of information which may be distributed over the transmissionline. This model makes it possible to provide a biunique correspondencebetween an object of the data base and an entity addressable by aconnection interface of an apparatus. Such correspondence is illustratedin tables I and II hereafter.

                  TABLE I                                                         ______________________________________                                        DISTRIBUTED DATA BASE                                                         OBJECT                                                                         ##STR1##                                                                      ##STR2##                                                                     ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        LOCAL ENTITY                                                                   ##STR3##                                                                     LOCAL CONFIGURATION OF THE OBJECT                                             Configuration-identification                                                  Key attribute                                                                 Description of the data                                                       L.sub.-- Identification                                                       Name                                                                          Class                                                                         Period                                                                        Data type                                                                     Description of the data                                                       Use                                                                           CONFIGURATION OF THE ENTITY                                                   Class (controlled automatic start).                                           "List Of" (references relative to the configuration of the                    data of an object for each object produced by the entity).                    "List Of.sup.≠ " (references relative to the configuration of an        object for each object known and not produced by the entity).                 ______________________________________                                    

As can be seen from table I, the frame of the objects of the data basecomprises a list of attributes for identifying the objects andsupporting specific variables of this object. This list may moreparticularly comprise:

An identification attribute L₋₋ I formed by an integer of 16 bits, whichserves for identifying the object in the transmission line. Itrepresents the identification used internally in the line and in thedata base.

A name attribute "A₋₋ name": this attribute, of character chain type,serves for identifying the objects between cooperating entities. suchidentification may also be used.

A class attribute "Class": this attribute indicates the class of theobject including a variable and a description.

A period attribute: this attribute contains an aperiodic value if theobject is not to be updated periodically, or the value of the requiredrefreshment period.

A data type attribute "Data₋₋ type": this attribute must contain thename of the data type. It defines both the semantics and the codingrules of the coded value attribute.

A valid attribute "Valid" which will contain a value signalling a faultif the object is not at the moment available for a consumer for anyreason, for example because of an absence of provider, or a modificationduring its definition. It should however be noted that an object may bevalid in the data base whereas it is invalid for a consumer, for examplebecause of a defect of the consumer.

A coded value attribute: this attribute must contain either the currentvalue of the object, coded according to the rules defined by the "Datatype" attribute or the "Indefinite" value. The current value is updatedperiodically or at random, depending on what is defined in the periodattribute. This attribute contains the last value sent over the linefollowing a message ID₋₋ DAT LPDU.

The information which has to be stored in each local entity and whichcan be used by the distributed data base is modelled locally, at thelevel of the connecting layer, in a given object configuration "localconfiguration of the object" including the following attributes (TableII):

a configuration and identification attribute which identifies the localconfiguration of the data of the entity,

a data description attribute which contains the static attributes of theframe of the objects of the data base, namely:

the identification attribute,

the name attribute "A₋₋ name",

the class attribute "Class",

the period attribute "Period",

the data type attribute "Data₋₋ type",

an "image description" attribute which contains the static attributes ofthe image data,

a utilization attribute (provider and/or consumer or neither of thesetwo modes).

The characteristic parameters of each entity are modelled in an objectconfiguration "entity configuration" which allow it to communicate withanother entity, such modelling comprising the following attributes:

a class attribute=automatic start, controlled start,

a "List of" attribute which must contain the list of the referencesrelative to the configuration of the data of an object, for each objectproduced by the entity,

a "List of" attribute which must contain the list of the referencesrelative to the configuration of an object for each object known and notproduced by the entity.

To each "controlled start" value included in the configuration of anentity, there corresponds a control register organized as a controlobject "control" consumed by the entity, this object comprising thefollowing attributes:

Key attribute (field data reference) which contains a local reference toan object consumed by the entity, and

Start attribute "Start" which serves for validating the introductionprotocol which will be defined hereafter in the description; thisattribute is sent to the network in a way similar to that of thepreviously mentioned coded value attribute.

It is then apparent that each object has a specific class. The onlyclasses differentiated in the mechanism proposed are: the VARIABLE andthe DESCRIPTION.

Updating and maintenance of the data base are provided by aconnectionless protocol. Each local entity maintains a local copy of acorresponding useful part of the data base and, when required, updatesthe part of the data base which it contains.

The main services rendered by the transmission line to the differentuser entities are control of the updating of the data base, access tothe local image of this data base and updating of the objects.

The data base is independent of the physical position of the dataproviders and consumers.

The relation between an apparatus and its data produced and consumed maybe modified without generating transformation of the data base.

In addition to a partial copy of the data base, each entity maintains adata image for each object produced which it consumes. This image, whichcontains the information for the transfer of an object to a device, ismodelled in a configuration comprising the following attributes:

a "Key", attribute which must contain a reference to an object used bythe device,

a "Use" attribute which must contain either the "consumer" value if thecoded value of the object is to be received by the entity or "Provider"if it is to be transmitted, a value Both indicating that the coded valueis to be received and transmitted, and a value indicating that the codedvalue is not to be transmitted or received,

a "Valid" attribute which must contain the value "False" if the objectis not locally available and "True" in the opposite case; the reasonsfor the invalidation comprise in particular the global invalidation ofthe object (validity attribute=False), or non conformity between thedescription of the object given by the transmitting entity and thedescription of the object desired by the local entity, and localfailures,

a "Next value provided" attribute: if the "Use" attribute of the imageis "Provider" or "Both", this attribute will contain either the nextvalue to be sent or the "indefinite" value; this value is updated by thelocal user and may be different from the coded value of the object; thevalue of this attribute must be transmitted to the line following aninstruction ID₋₋ DAT LPDU by thus updating the coded value attribute ofthe object.

Access to the data base is provided by the Bus Arbitrator which forms asingle entity guaranteeing that updating of the data base takes place inaccordance with the period and precision requirement specified by theuser entities.

The difficulty, in such a system, is to guarantee that the producer andconsumer of the same data are agreed about the rules of use of thevariable, about its syntax and its semantics, whatever the eventsdisturbing the network (power cut of a station, modification of theconfiguration of a station, insertion of a new station): in no case musta variable transmitted as a chain of bits be interpreted by the receiveras a floating number or anything else different from a bit chain.

The solutions usually used for guaranteeing the consistency betweentransmitter and receiver consist:

in sending at the same time into the network, for each exchange, thevalue of the variable and its syntactic or semantic description; thishas the drawback of loading the network and losing the passband, whichis very often unacceptable;

in negotiating, before any exchange of variables, the context ofcommunication between the communicating entities, by establishing alogic connection between transmitter and receiver; this has the drawbackof requiring a complex connection mechanism and it must be establishedfor any transmitter-receiver association (several possible connectionsper product); it proves that the cost of the connection protocols andthe simultaneous maintenance of several connections is prohibitive forsimple products connected to the transmission line, which is contrary tothe desired aim.

The invention has more particularly as object to solve the problem ofconsistency guarantee, using a protocol without previous contact, oracquittal, designed so as to economize the passband of the transmissionline.

For this, use was first made of a central entity knowing theconfiguration of the network (connected products and exchanged variablesand capable of verifying the configurations of the connected productsbefore bringing them into service on the network and, possibly, ofremotely loading this configuration. This entity may be the mastercontroller if it exists, or a dedicated independent entity, which mustremain permanently on the network.

However, this solution has multiple drawbacks:

it requires an entity controlling all the configurations of the network.Now, even if, at a certain moment of the design stage, an overall viewof the network is necessary, the configuration information may then bedivided between different entities (several controllers on the network,several constructors), and it may be penalizing to then group togetherthis information in a single entity.

Even if the central entity exists in the design phase, it is penalizingto require a permanent connection of this entity for managing the eventsdisturbing the network (power cut, replacement of defective product, . ..).

This is why the invention proposes carrying out such consistencychecking before any use, even in the case where there has previouslybeen a design office check at generation, such a check in particularallowing communication between the globally configured entities and,possibly, other locally configured entities (addition of new entities ina globally configured network).

Of course, such consistency checking will have to take place using thenon optional services of the layer connecting the entities, namely usingthe information exchange mechanism by broadcasting without acquittal.

When an entity is brought into service, this check will take placebetween a producer entity and consumer entities, via the line.

It should however be noted that this check does not guarantee that allthe entities concerned by an object have the same specification of thisobject its only purpose is to guarantee that only the entities havingthe same specification of this object will participate in the exchangeof the object.

Considering the foregoing, the invention proposes generally a method fortransmitting information by means of a line capable of effecting aseries-multiplexed type transmission between entities capable oftransmitting and/or receiving information from and to the line, and toprovide physical interfaces between application interfaces and the line,so that each entity connected to the line may have access to all theinformation flowing over the line, the whole of the data exchanged beingmodelled by a distributed data base, the updating and maintenance ofwhich are ensured because each entity keeps and updates a local copy ofthe corresponding useful part of the data base which it contains.

According to the invention, this method is more particularlycharacterized in that, whenever an entity is brought into service, itcomprises a consistency check for guaranteeing that the producer andconsumer entities interpret a piece of information in the same way, thisconsistency check comprising the generation of validation information byeach of the entities, this information signifying an invalid state atthe moment the method is implemented and only signifying a valid stateif this entity recognizes a specification of an object of the data basetransmitted over the line and in that only the entities generatingvalidation information signifying a valid state may participate in theexchange of the value of the object.

Taking into account the fact that the validation and invalidation phasesuse a non acquitted exchange service, it is thus possible to avoidhaving to use an acquittal system which is usually expensive.

Advantageously, the entities generating validation information in thevalid state for the same object will present the same specification,this common specification being frozen and able to be exchanged at anytime to allow new entities to participate in the exchange.

Moreover, the specification transmitted over the line within theframework of this consistency check will be provided by the entitycomprising the global specification of the object, this specificationbeing then delivered in the form of aperiodic or possibly periodic data.

It is clear that as soon as the local description of an entity ismodified or likely to be modified (reset, power resumption, localmodification, . . .), this entity withdraws from the exchange.

In the case where this entity is a consumer, it may withdraw withoutdisturbing the other participating entities (only its validationinformation is in the invalid state).

A producer entity which transmits a validation signal in the invalidstate must suspend updating, not only of its buffer memory serving fortransmission (transmission buffer), but also buffer memories serving forreception (reception buffer) of the receiving entities. For that, itinvalidates its transmission buffer at the level of the connectionlayer, which invalidates updating of the value in the network. Suchinvalidation is detected by the receiving entities. Following suchdetection (which is guaranteed for any receiver), any receiving entityinvalidates the object locally.

To invalidate an object, a consumer entity has two pieces ofinformation:

the detection of an invalidation message of the network (invalidationRP₋₋ DAT) which is incorrect or absent after reception of a message ID₋₋DAT identifying the frame of the object, the message RP₋₋ DAT of thenetwork having to contain the parameters of the object, it beingunderstood that invalidation of a producer entity not followed by atransmission error generates an invalidation RP₋₋ DAT message (producerentity in service, data invalid) or an RP₋₋ DAT absent (no frame)(producing entity out of service).

optionally, a signal (time out) monitoring refreshment of the network(promptitude) which also takes into account the absence of refreshmentdue to transmission errors. Such transmission errors then cause either aRP₋₋ DAT absent or a RP₋₋ DAT incorrect, or the absence of sequence ID₋₋DAT/RP₋₋ DAT.

The consumer entity obligatorily invalidates an object followingreception of an invalidation RP₋₋ DAT.

The producer entity imposes the global invalidation by generatingseveral invalidation RP₋₋ DAT messages (at least 3) so as to be surethat each consumer entity will detect at least one invalidation RP₋₋DAT.

Modification of the specification of an object while guaranteeing theconsistency takes place in two steps:

a first step consisting in invalidating the object in the whole of theentities concerned, beginning by the producer,

a second step which takes place when it is certain that the entitiesconcerned have invalidated the object, this step consisting inintroducing the object with a new description.

The broadcasting of a specification over the network must be made by oneentity and only one. The simplest thing is then for this specificationto be broadcast by the entity producing the object.

There may however exist simple products (TOR input modules) for whichthe storage and control of this information are of prohibitivecomplexity. It is possible to store the specification elsewhere (forexample in the automaton) provided that the invalidation rules arestrictly respected. The available stored specification must at all timesconform to the value transmitted by the producer and a possiblemodification of the specification must follow invalidation by theproducer.

At the time of an automatic or controlled start, the introductionalgorithm may be initiated by each entity following a local event such,for example, as power resumption, after cut off or re-setting. Thisintroduction may take place either automatically "automatic start mode"or after the authorization of a third party "controlled start mode".

The operating mode is defined by the "start" class attribute of theobject and the authorization is given by the writing of a control wordrepresented by the control attribute of the device and transmitted bythe "command" identifier.

The "controlled start" mode makes it possible for an applicationprogramme, specialized in the configuration control to read or remotelyload the configuration of the data, the data and the image of the datafor each entity, to make an overall check and, only afterwards, to causestarting of the entity. It provides additional safety by controlling theidentifier duplications of the data before collision in the network.

The specification broadcast over the network contains (among otherthings) the network period of the data, which must be consistent withthe network period guaranteed by the Bus Arbitrator in its scanningtable.

It is possible to use an optional application programme, related to theBus Arbitrator, to check such consistency and take a decision in thecase of an anomaly: either to withdraw the data from the scanning table,or to modify the scanning table accordingly.

As mentioned above, the invention provides a protocol to be executed byany data producing or consuming entity with a view to its being broughtinto service on the network, while guaranteeing the consistency of thedescription between transmitting entities and consuming entities.

Embodiments of this protocol will be described hereafter by way of nonlimitative examples, with reference to the accompanying drawings inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of an introduction protocol to be executed foreach data produced when the description is stored in the producerentity;

FIG. 2 is a flowchart of an introduction protocol which is to beexecuted for each data produced when the description is not stored inthe producer entity (in the case where the producer entity is not richenough to contain its description);

FIG. 3 is a flowchart of an introduction protocol to be executed foreach data consumed.

It should first of all be noted that each data produced by the producerentity implies the execution of an algorithm. Furthermore, the entitymust manage an identifier produced for the value of each data andanother identifier for the specification of this data.

The producer entity must further be capable of generating aperiodicupdating requests (instruction L₋₋ UPDATE=request instruction to theconnection layer to effect aperiodic updating).

In the case where the producer entity possesses the specification of thevariable, the start phase of the algorithm takes place at the time of alocal situation (start, reset, power resumption, configuration) suchthat the entity cannot guarantee the consistency of its state with thatof its correspondents, in this case:

the attribute "Valid" of the image data bears the mark "False",

the transmission buffer in the connection layer of the entity containingthe value of the data is invalid (writing instruction in buffer L₋₋ PUT,empty),

which causes transmission over the network of an invalidation RP₋₋ DATmessage in response to a message ID₋₋ DAT (frame transmitted by the BusArbitrator which provides means for access to the entity possessing theassociated data).

At the same time, the transmission buffer of the connection layerassigned to the entity, which contains the specification of the data, isalso invalid so as to avoid the simultaneous running of the introductionprotocol by a consumer.

If the class of the entity ("Start" class attribute of the entity) is"automatic start" or if this class is "ordered start" and if the controlword ("Entity control" attribute of the entity) allows starting, thealgorithm executes a following phase of the algorithm consisting inguaranteeing the invalidation (transmission of a "flag" invalidationsignal) in all the receiver entities. One possible method is to transmitseveral (recommended value: 3) messages RP₋₋ DAT having an emptycontent. Several algorithms can be used by the producer entity: the onlyrequirement is that these algorithms generate at least severalinvalidation messages RP₋₋ DAT in a given time.

FIG. 1 shows one example of such an algorithm to be executed for eachdata produced when the description is contained in the producer entity.

In this example, in the "initial state" block 1, the image of the datais invalid.

The next step is then reading the class attribute "Class" (block 2). Inthe case where this attribute contains the automatic start information"Auto-start" (block 3), the system passes automatically to the nextstep. On the other hand, if this information is "start ordered" (block4), the system will only pass to the next step after the transmission ofa control instruction ("Start control=True") (block 5).

The next step must comprise the transmission of a given number(recommended value: 3) of consecutive invalidation messages RP₋₋ DAT(block 6). These messages may be sent by the system in response to thecyclic scanning of the variable by the Bus Arbitrator or may be causedby an explicit request of the system (in the case where the variable isnot scanned periodically, or periodically with a long period), by theinstruction "L₋₋ UPDATE" (block 7). Transmission of the invalidationmessage is signalled by the indication L₋₋ SENT. The system counts theindications L₋₋ SENT (block 8) and remains in the invalidation phase aslong as their number is less than the predetermined value (block 9).

The next step consists in updating the buffer of the connection layer byintroducing a description of the new variable (block 10). This is thenexecuted after the transmission of the instructions L₋₋ PUT (acquisitionof the description of the variable) and L₋₋ UPDATE (updating of thedescription of the variable).

Following transmission of the new description signalled by theindication L₋₋ SENT (block 11), the system proceeds to update andvalidate (passage from the attribute "Valid" of the data image to thevalue "True") the image of the new data (block 12).

In the case where, for a local reason, the variable is invalidated(local invalidation) (block 13), the system reinitiates the algorithmfrom the beginning (i.e. from the initial state=image of the invaliddata). This procedure is begun for each local event casting a doubt onthe consistency of the local specification with respect to the network.

In the case where the producer entity does not possess the specificationof the variable, an algorithm must be executed for each data produced bythis entity, which must then manage an object identifier for this valueand a consumed identifier for the specification of this value.

In this case, the producer entity does not have to manage a periodicupdating requests(instruction L₋₋ UPDATE) for this function.

An entity of the network manages the specification of the data and mustthen provide an object identifier for the specification.

In a way similar to the preceding one, the algorithm starts, followinglocal situations (start, reset, power resumption, configuration, . . .)such that the entity cannot guarantee the consistency of its state withthat of its correspondents in the network, the attribute "Valid" of thedata image indicates the information "False".

The transmission buffer in the connection layer of the entity containingthe value of the data is invalidated (instruction for writing in bufferL₋₋ PUT, empty), which causes the transmission over the network of aninvalidation message RP₋₋ DAT in response to a message ID₋₋ DATtransmitted by the Bus Arbitrator.

This invalidation is monitored by the entity which manages thespecification of the data, which accordingly invalidates thetransmission buffer containing the specification of the data (in orderto avoid the simultaneous running of the introduction protocol of thenew data by a consumer).

The way in which the entity managing the specification is informed ofthe invalidation of the producer depends on a local applicationprogramme which ensures the detection of an invalidation signal RP₋₋DAT, which monitors the state of the station, etc. . .

If the class of the station ("Start" class attribute) of the entity is"automatic start", or if this class is "controlled start" and if thecontrol word ("entity control" attribute) allows starting, the entityexecutes the next phase of the algorithm.

This phase consists then in guaranteeing the invalidation by theinvalidation signal in all the receivers, by transmitting at least thepredefined number of invalidation signals RP₋₋ DAT, after invalidationof the value and of the specification.

Several algorithms are possible between the producer and the entitymanaging the specification: the only requirement is that thesealgorithms generate at least the pre-defined number of invalidationsignals RP₋₋ DAT in a given time.

One example of such an algorithm is illustrated in FIG. 2.

As in the preceding example, this algorithm starts from an "initialstate" block (block 15) in which the data image is invalid, then asecond step including reading of the class attribute (block 16).

In the case where this attribute is "automatic start" (block 17), thesystem will pass to the next phase. On the other hand, if this attributeis "start ordered" (block 18), the system will only pass to the nextstep following the transmission of a control instruction ("startcontrol=True") (block 19).

This step then comprises the invalidation by the producer entity of itstransmission buffer (block 20). The entity managing the specification,after invalidation of this specification, generates at least thepre-defined number of aperiodic requests on the value, which willgenerate an invalidation RP₋₋ DAT (instruction L₋₋ SENT: invalidationdata signal) (block 21).

The phase which follows this invalidation step is a step for updatingthe transmission buffer containing the specification of the data withthe new description by an instruction L₋₋ PUT, which description is inthe entity managing the specification. A request for aperiodic updatingof this identifier is managed by the instruction L₋₋ UPDATE, adescription in this entity which causes broadcasting of thespecification over the network.

The algorithm makes sure that this specification has been received bythe producer entity (block 22, block 23), if not it passes to theinvalidation phase (block 20).

On reception of the specification broadcast through the network, theproducer processes the specification according to a local algorithmcomparable to that used by a receiver entity.

Depending on the result of the processing, it validates (or not) (block25) the value identifier of the data by updating the transmission buffer(block 24) by an instruction "L₋₋ PUT value" and marks the validationattribute of the image data with the value "True".

As mentioned above, for each data consumed, the consumer entity mustimplement an introduction algorithm.

For this, the entity must manage an identifier produced for the valueand an identifier consumed for the specification of each data.

The consumer entity may or may not be capable of managing aperiodicupdating requests (following transmission of an instruction L₋₋ UPDATE).

Such as shown in FIG. 3, the introduction algorithm starts from aninitial state (block 30) in which the validation attribute of the imageof the data is in the invalid or false state.

This occurs in the case of local situations such as start, reset, powerresumption, configuration, . . . such that the entity cannot guaranteethe consistency of its state with that of its correspondents. Updatingin the reception buffer is invalidated.

If the class "Class" (block 31) of the entity (starting class attributeof the entity) is "Auto-start" (block 35) and if the control word("Command Start" attribute of the entity) allows starting, the systemexecutes the next phase of the algorithm.

This phase consists in waiting for the broadcasting of the specification(block 35) (request instruction for broadcasting of thespecification=L₋₋ UPDATE) (block 36) and at the time of reception"Receive" of this specification (block 37) processing this specificationin accordance with an algorithm of its own and comparing (block 38) itwith its own configuration information. If it accepts (block 39) thespecification received from the network, it validates (block 40) thereception of the value of the data (block 42) and marks the attribute ofthe image of the data with the value "True", if not it remains in thesame state.

The algorithm for processing the specification depends on theimplementation and may for example result from the following threecases:

The entity possesses a complete local specification. It compares thespecification provided by the network with its own local specificationand validates the data (block 40) if these two specifications areidentical and leaves it invalid (block 41) if these specifications aredifferent.

The entity possesses a partial specification. In this case, it comparesthis specification with the corresponding parts of the specificationreceived from the network and completes the missing parts from thespecification delivered by the network. In this case, configurationprocessing of the entity may be made necessary.

The entity does not possess a specification. In this case, it acceptsthe specification transmitted by the network and configures itselfaccordingly.

It should be noted in this connection that it is not necessary for theentity to store the specification transmitted by the network. It issufficient for it only to guarantee processing in conformity with thisspecification.

Furthermore, the specification request on the initiative of a consumerentity is particularly useful in the case of bringing this consumerentity into service in an operating network. If this entity is notcapable of generating aperiodic requests, it will then be necessary touse an application programme monitoring use of the station forgenerating the request for broadcasting the specification.

An abnormal response (silence or invalidation data) to a specificationmeans that the producer entity is invalid. The consumer entity thenplaces itself in a stand-by condition waiting for the producer to bebrought into service.

A consumer entity will invalidate data causing passage from theattribute of the value "Valid" to the value "False" on reception of aninvalidation message RP₋₋ DAT or possibly following the detection ofseveral consecutive errors on reception.

What is claimed is:
 1. Method for transmitting information between aplurality of producer and receiver entities of a control and checkingsystem of an industrial equipment,comprising sensors as producingentities, actuators as receiving entities and programmable controllersas producing/receiving entities, said information being transmitted bymeans of a series-multiplexed type transmission line on which saidentities may be connected to form a network and brought into service soas to transmit information on said line and to have access to all theinformation flowing on said line, said information being modelled by adistributed data base including a collection of data grouped together soas to form a plurality of objects, each having a specification and avalue, each entity comprising a memory storing a copy of thespecification and the value of at least one object which concerns it,wherein, for each new entity brought into service on the line and whichprocesses and consumes one of said objects, said method comprises thefollowing steps:a step of transmitting on the line the specification ofsaid object, a step of receiving said transmitted specification by everyentity concerned by said object, a step of comparing in each of saidentities the received specification with the specifications included inthe memory of said entity, a step of generating an invalidationinformation of the object in one of said entities when the comparisoneffected in this entity reveals a difference, a step of generating avalidation information of the object in one of said entities when thecomparison effected in this entity reveals an identity, only the entitywhich has generated a validation information being habilited toparticipate in an exchange of the value of the object.
 2. Methodaccording to claim 1, wherein the entities generating validationinformation for the same object have a common specification whichcorresponds to said transmitted specification and which is able to beexchanged at any time so as to allow new entities t participate in theexchange.
 3. Method according to claim 1, wherein,when transmitting aninvalidation information, one producer entity suspends the updating notonly of its own memory, but also of the memory of said receiverentities.
 4. Method according to claim 1, wherein the invalidation of anobject, by a receiver entity takes place by the reception, by saidreceiver entity, an invalidation information which comes from anotherentity.
 5. Method according to claim 1, wherein in order to invalidatean object, a receiver entity generates a signal monitoring a refreshmentof the network.
 6. Method according to claim 1, which further comprisessequence modifying an object, while guaranteeing the consistency, saidsequence comprising the following two steps:a first step of invalidatingthe object in all the entities concerned, beginning by the producer; asecond step which takes place when the entities concerned haveinvalidated the object, this step consisting in introducing the objectwith a new specification.
 7. Method according to claim 6, characterizedin that broadcasting over the transmission line of the new specificationis effected by one entity and only one.